It is known that diesel soot filters having a porous wall permit gaseous components of the exhaust gas to pass, while they prevent the passage of solid particles which result, above all, from coagulation of carbon molecules and heavy hydrocarbons.
The soot particles deposited in the diesel soot filter and, in the course of operation, progressively clogging the diesel soot filter can be decomposed by thermal (burning), catalytic, or other processes to regenerate the diesel soot filter.
Thermal regeneration with the engine running, e.g. during operation of a vehicle equipped with the same, may cause an uncontrolled rise of the reaction speed of the combustion of the particles collected in the diesel soot filter under stochastic conditions when the regeneration is released automatically. That may lead to an inadmissible temperature increase and result in partial or total fusion or destruction of the diesel soot filter.
It has been suggested to measure the temperature of the exhaust gas downstream of the diesel soot filter (DE 38 06 219 A1) to avoid uncontrolled combustion. If a predetermined maximum admissible temperature is exceeded in this case valves upstream and downstream of the diesel soot filter are actuated by means of an electronic unit so that all of the exhaust gas will be discharged through a bypass circumventing the diesel soot filter. Thus the diesel soot filter, temporarily, is disconnected entirely from the exhaust gas stream.
Although operation through the by pass makes up only a small percentage of the overall operating time of the engine, muffling equipment is need to dampen the annoying noise which is created during the bypass operation. Moreover, it is undesirable from the ecological point of view to discharge unscrubbed exhaust gases without filtering into the atmosphere even for a short time, as occurs in bypass operation.
It is likewise known (CH 663 253 A) to divide a particle filter in the exhaust gas tract of an internal combustion engine, especially one with exhaust gas supercharging, into two sections connected in parallel, namely one thermally well insulated "high temperature flow zone" and one "low temperature flow zone". By means of a control flap, exhaust gas will flow through the low temperature flood only at low engine load and through both flow zones at high engine load, by corresponding adjustment of the control flap. The results hereof, apart from frequent particle combustion, is that the exhaust gas supercharger connected downstream of the exhaust gas tract always is fed quickly with exhaust gas of sufficient temperature in order to prevent the so-called "turbo hole" upon depression of the accelerator pedal. However, protection against uncontrolled burn off of deposited particles in the flow zones cannot be achieved by the measure according to the Swiss patent.